This invention relates to electromagnetic clutches and, in particular to clutches, for use in driving refrigerant compressors for automobile air conditioning systems.
FIG. 1 illustrates, a known electromagnetic clutch which is used between the engine and the compressor for selectively driving the compressor; and includes a pulley 1 which is mounted on a bearing 2 mounted on a tubular extension 3 of a compressor housing 4 and which is rotated by a belt shown by an dotted line from the automobile engine (not shown), as disclosed in, for example, in U.S. Pat. Nos. 3,044,594 and 3,082,933.
Pulley 1 is provided with a plurality of concentric annular magnetic pole faces 1a at an axial end thereof. A drive shaft 5 of the compressor extends through tubular extension 3. A hub 6 is fixed to the extending terminal end of the drive shaft 5, and an annular armature plate 7 is joined by leaf springs 8 to hub 6 so that the armature plate 7 faces the annular concentric pole faces with an axial space therebetween. An electromagnet 9 is mounted on tubular extension 3, and is stationarily disposed within an annular hollow portion formed in pulley 1 to supply magnetic flux for attracting armature plate 7 to magnetic pole faces 1a.
Thus, when electromagnet 9 is energized, drive shaft 5 is rotated together with pulley 1 by the engine output, and when electromagnet 9 is not energized, pulley 1 is rotated by the engine but the compressor is not driven.
In such known electromagnetic clutches, the pulley has been formed as a body of magnetic material such as steel by forging followed by machining. However, the resultant pulley is relatively heavy so that the total weight of the compressor is increased. This means that the load on the driving power source, the automobile engine, is increased. Furthermore, since the pulley has a relatively complex shape, it takes a long time to form the pulley. That is, the pulley is formed through a long forging process and is finished to accurate dimensions through a machining step. In the machining step, a large amount of material is removed. Therefore, in the known method for producing the pulley, much material is wasted. Thus, the cost of the electromagnetic clutch is increased.
Referring to FIG. 2, another known method of producing the pulley is to seperately produce an annular magnetic main body 11a and an annular V-groove member 11b by a press forming method, both of which are welded to one another after the main body 11a is fitted into the annular V-groove member 11b. In this method, it is difficult to provide that the used welding agent is uniformly deposited between the main body and the V-groove member. Furthermore, the V-groove member is often thermally deformed in the welding step, and the resultant pulley is thereby unbalanced.